1. Field of the Invention
The present invention relates generally to a mobile communication system that supports multimedia service including voice and data services, and in particular, to an apparatus and method for transmitting and receiving information indicating a forward data rate between an MS (Mobile Station) and a BS (Base Station).
2. Description of the Related Art
A typical mobile communication system, particularly CDMA (Code Division Multiple Access) mobile communication systems including synchronous CDMA (IS-2000) and asynchronous UMTS (Universal Mobile Telecommunication Service) (Wide CDMA) support an integrated service of voice, circuit data, and low-rate packet data (for example, at or below 14.4 kbps). The growing user demands for high-speed packet data service such as Internet access, however, have brought about development of corresponding mobile communication systems. CDMA 2000 1x EV-DO (Evolution Data Only) supports a 2 Mbps or above high-speed packet data service by assigning resources for a voice service to a data service, but has the shortcoming that it does not support the voice service and the data service concurrently.
To satisfy a need for a mobile communication system supporting both an existing voice service and a high-speed packet data service, 1x EV-DV (Evolution Data and Voice) has been proposed. In 1x EV-DV, a BS schedules transmission of packet data and determines transmission parameters according to forward channel quality. Specifically, the BS selects one of a plurality of MSs in communication with the BS every slot, which has the best forward channel quality, transmits packet data to the selected MS, and determines transmission parameters (e.g., data rate, code rate, and modulation order) according to the forward channel quality of the selected MS.
The carrier-to-interference ratio (C/I) of an F-CPICH (Forward Common Pilot Channel) from the BS measured in each MS is essential to determining the forward channel quality of the MS. The MS reports the C/I measurement to the BS on an R-CQICH (Reverse Channel Quality Indicator Channel). The BS schedules transmission of packet data on F-PDCHs (Forward Packet Data Channels) and determines transmission parameters according to C/Is from MSs.
FIG. 1 is a block diagram of a conventional transmitter for transmitting forward channel quality information to a BS in an MS. Referring to FIG. 1, the C/I of an F-CPICH received from a BS (a sector in the case of a sectored BS) in communication is measured, quantized, and converted to a corresponding binary 5-bit CQI (Channel Quality Indicator) symbol every 1.25-ms time slot. An encoder 110 encodes the CQI symbol at a code rate of 5/12 (R= 5/12) and outputs a 12-bit CQI sequence. A Walsh cover code generator 120 generates a Walsh cover code of length 8, Wi8 (i=0, . . . 7) according to a BSI (Best Sector Indicator) indicating a BS having the best forward channel quality among BSs that the MS can sense.
A Walsh cover 130 generates a 96-bit Walsh covered symbol by multiplying the code sequence by the Walsh cover code Wi8. A signal mapper 140 maps the 96-bit symbol to a symbol with +1s and −1s. A Walsh spreader 150 spreads the output of the signal mapper 140 with a Walsh code assigned to a CQICH, W1216 prior to transmission.
FIG. 2 is a timing diagram for transmission and reception of forward channel quality information in the BS and the MS. Referring to FIG. 2, the MS transmits to the BS a CQI symbol indicating the C/I of the F-CPICH from the BS in each slot of an R-CQICH. The BS receives the CQI symbol after some propagation delay and uses it for PDCH scheduling and parameter determination. The propagation delay is time required for the CQI symbol to go through the air. In FIG. 2, a CQI symbol received in an nth slot of the R-CQICH is applied to an (n+1)th slot of an F-PDCH after some processing delay. The processing delay refers to time required to calculate the C/I of the F-CPICH from the CQI symbol, schedule packet data transmission, and determine transmission parameters.
In the above conventional method of transmitting and receiving forward quality information, the reverse traffic capacity of the BS is remarkably reduced because a plurality of MSs transmit CQI symbols in each slot to the BS. Moreover, R-CQICHs from the MSs interfere with one another, resulting in the increase of interference across the overall system.